The answer is A
The bacteria that cause disease are known as pathogens. The term pathogen is used to refer to all types of disease causing microorganisms. These include bacteria, fungi, protozoa and fungi.
Bacteria. Microscopic organisms that come in many shapes and sizes. Some bacteria that cause disease in man are Salmonella typhi which causes typhoid and Streptococcus pyogens which causes sore throat.
Virus. A virus is a microscopic entity much smaller than even bacteria and can only exist inside a host such as a cell. It cannot live on its own. Some viruses that cause disease are HIV which causes AIDS and Rhino virus which causes colds.
Fungi. These are a group of unicellular or multicellular microscopic organisms that live by feeding on organic matter. A type of fungus that causes disease is Trichophyton mentagrophyte which is responsible for athlete's foot.
Protozoa. A group of one celled organisms which live in water. Entamoeba histolytica is a protozoa, an amoeba which causes amoebic dysentery in man.
